Question

Worker A takes 8 hours to do a job. Worker B takes 10 hours to do the same job. How long should it take both A and B, working together but indepently, to do the same job?

Answer 1

A does in 8 hours. Hence, he does 1/8 part of job in 1 hour.
Similarly, B does 1/10 of job in 1 hour.
When they will work together on same job, they will do [(1/8)+(1/10)] of the job in one hour.
1/8+1/10⇒ (5+4)/40
              ⇒  9/40

They do 9/40 of job in 1 hour. 

So, they do the job in 40/9 days. {40/9 days= 4.4 days or 4 days and 6 hours)
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Answer 2

1/8 +1/10
5+4/40
9/40
it will reciprocal so it will be40/9 that is 9*4/40 days


hope it will help u